Vertical Gate All Around (VGAA) Devices and Methods of Manufacturing the Same

ABSTRACT

Vertical gate all around (VGAA) devices and methods of manufacture thereof are described. A method for manufacturing a VGAA device includes: exposing a top surface and sidewalls of a first portion of a protrusion extending from a doped region, wherein a second portion of the protrusion is surrounded by a gate stack; and enlarging the first portion of the protrusion using an epitaxial growth process.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/872,361, entitled “Vertical Gate All Around (VGAA) Devices andMethods of Manufacturing the Same,” filed on Jan. 16, 2018, which is adivisional of U.S. patent application Ser. No. 14/660,542, entitled“Vertical Gate All Around (VGAA) Devices and Methods of Manufacturingthe Same,” filed on Mar. 17, 2015 (now U.S. Pat. No. 9,899,489, issuedFeb. 20, 2018), which is a continuation-in-part of U.S. patentapplication Ser. No. 14/621,628, entitled “Vertical Gate All Around(VGAA) Devices and Methods of Manufacturing the Same,” filed on, Feb.13, 2015, which patent applications are incorporated herein byreference.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologynodes in pursuit of higher device density, higher performance, and lowercosts, challenges from both fabrication and design issues have resultedin the development of three-dimensional designs, such as a vertical gateall around (VGAA) transistor. A typical VGAA transistor enables enhancedcontrol of the charge carriers along the lengthwise direction through acomplete encirclement of the channel region of a semiconductor nanowireby a gate dielectric and a gate electrode. The VGAA transistor has areduced short channel effect (e.g. compared to a planar transistor),because the channel region may be surrounded by the gate electrode sothat an effect of the source/drain region on an electric field of thechannel region may be reduced (e.g. relative to a planar transistor).

However, VGAA transistors may suffer from high contact resistance andhigh parasitic capacitances. As such, improvements are needed in themanufacturing processes in order to manufacture VGAA transistors withlower contact resistances and lower parasitic capacitances.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A to 1H show a process flow illustrating various intermediarysteps of manufacturing a semiconductor device having a first verticalgate all around (VGAA) device and a second VGAA device, in accordancewith one or more embodiments.

FIGS. 2A to 2D show top-down and cross-sectional views of drain layersand enlarged drain regions extending from surfaces of the drain layers,in accordance with one or more embodiments.

FIGS. 3A and 3B show top-down views illustrating various shapes ofprotrusions, in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and stacks are described belowto simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIGS. 1A to 1H show a process flow illustrating various intermediarysteps of manufacturing a semiconductor device 100 having a firstvertical gate all around (VGAA) device 102 and a second VGAA device 202,in accordance with one or more embodiments. As an example, the firstVGAA device 102 may be an NMOS VGAA device, while the second VGAA device202 may be a PMOS VGAA device.

The semiconductor device 100 may comprise a semiconductor substrate 104over which the first VGAA device 102 and the second VGAA device 202 areformed. The semiconductor substrate 104 may be a semiconductor wafer andmay comprise silicon (Si); germanium (Ge); a compound semiconductorincluding silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide, indium arsenide, and/or indium antimonide; an alloysemiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP,and/or GaInAsP; or combinations thereof. The semiconductor substrate 104may be a bulk semiconductor substrate, a semiconductor-on-insulator(SOI) substrate, a multi-layered or gradient semiconductor substrate, orthe like.

The semiconductor device 100 may include a first doped region 106 and asecond doped region 206 laterally adjacent to and separated from thefirst doped region 106. The first doped region 106 may be a part or aportion of the first VGAA device 102, while the second doped region 206may be a part or a portion of the second VGAA device 202. The firstdoped region 106 may have a first conductivity, while the second dopedregion 206 may have a second conductivity different from the firstconductivity. For example, as described above, the first VGAA device 102and the second VGAA device 202 may be an NMOS VGAA device and a PMOSVGAA device, respectively. In such an embodiment, the first doped region106 may comprise a semiconductor material (such as silicon, germanium,silicon germanium, combinations of these, or the like) that containsN-type dopants (such as phosphorous or arsenic), while the second dopedregion 206 may comprise a semiconductor material (such as silicon,germanium, silicon germanium, combinations of these, or the like) thatcontains P-type dopants (such as boron or gallium).

The first doped region 106 and the second doped region 206 may beseparated from each other by an isolation feature 108 (e.g.shallow-trench isolation feature). The isolation feature 108 maycomprise an insulating material such as a dielectric material (e.g.silicon oxide or the like) and may serve to electrically isolate thefirst VGAA device 102 and the second VGAA device 202 from each other.The isolation feature 108 may be formed between the first doped region106 and the second doped region 206 by etching a recess in the firstdoped region 106 and/or the second doped region 206 and filling therecess with the insulating material using, for example, aspin-on-dielectric (SOD) process, or any other suitable process.

The semiconductor device 100 may include first protrusions 110 (e.g.disposed over and extending from the first doped region 106) and secondprotrusions 210 (e.g. disposed over and extending from the second dopedregion 206). The first protrusions 110 may be a part or a portion of thefirst VGAA device 102, while the second protrusions 210 may be a part ora portion of the second VGAA device 202. In the embodiment shown in FIG.1A, only two first protrusions 110 and only two second protrusions 210are shown as an example. However, in other embodiments, the number offirst protrusions 110 and/or the number of second protrusions 210 may beless than two (e.g. one) or more than two (e.g. three, four, or more).The first protrusions 110 and/or the second protrusions 210 may beshaped as nanowires. In other words, the first protrusions 110 and/orthe second protrusions 210 may have a substantially circular shape, e.g.when viewed in a top-down view. Alternatively, the first protrusions 110and/or the second protrusions 210 may be shaped as bars or fins, e.g.when viewed in a top-down view. These embodiments are described below ingreater detail in respect of FIGS. 3A and 3B.

Referring to the first VGAA device 102, each of the first protrusions110 may be a multi-layer semiconductor substrate comprising a sourcelayer 110 a, a channel layer 110 b, and a drain layer 110 c. In aparticular embodiment, at least a portion of the source layers 110 a,the channel layers 110 b, and the drain layers 110 c of the firstprotrusions 110 form the source regions, channel regions, and drainregions of the first VGAA device 102, respectively.

The source layers 110 a, the channel layers 110 b, and the drain layers110 c may comprise any suitable semiconductor material, such as silicon,germanium, silicon germanium, combinations of these, or the like. Forexample, in an embodiment, each of the source layers 110 a, the channellayers 110 b, and the drain layers 110 c comprise doped silicon.However, in another embodiment, the channel layers 110 b may comprisedoped silicon, while the source layers 110 a and the drain layers 110 ccomprise doped silicon germanium. In some embodiments, the source layers110 a may be formed by patterning a portion (e.g. an upper portion) ofthe first doped region 106. Consequently, in such embodiments, thesource layers 110 a may comprise a similar semiconductor material as thefirst doped region 106.

The semiconductor material of each of the source layers 110 a, thechannel layers 110 b, and the drain layers 110 c also comprises dopantsthat cause the source layers 110 a, the channel layers 110 b, and thedrain layers 110 c to have the same conductivity as the first dopedregion 106 (e.g. the first conductivity). For example, the first VGAAdevice 102 may be an NMOS VGAA device and, consequently, the sourcelayers 110 a, the channel layers 110 b, and the drain layers 110 c ofthe first protrusions 110 may be doped with N-type dopants such asphosphorous or arsenic.

In an embodiment, the dopant concentration of the first doped region106, the source layers 110 a, and the drain layers 110 c may besubstantially equal to one another and may, at the same time, be greaterthan the dopant concentration of the channel layers 110 b. For example,the dopant concentration of the first doped region 106, the sourcelayers 110 a, and the drain layers 110 c may be in a range from about1×10¹⁹ cm ⁻³ to about 1×10²² cm ⁻³ or even greater, while the dopantconcentration of the channel layers 110 b may be less than about 1×10¹⁸cm⁻³. In such an embodiment, the drain layers 110 c may be highly dopeddrain regions of the first VGAA device 102.

In another embodiment, the dopant concentration of the first dopedregion 106 and the source layers 110 a may be substantially equal toeach other and may, at the same time, be greater than the dopantconcentration of the channel layers 110 b and the drain layers 110 c.For example, the dopant concentration of the first doped region 106 andthe source layers 110 a may be in a range from about 1×10¹⁹ cm⁻³ toabout 1×10²² cm⁻³ or even greater, while the dopant concentration of thechannel layers 110 b and the drain layers 110 c may be less than about1×10¹⁸ cm⁻³. In such an embodiment, the drain layers 110 c may lowly ormoderately doped drain regions of the first VGAA device 102.

The first doped region 106 and the first protrusions 110 may be formedby epitaxially growing semiconductor material (e.g. using a firstepitaxial growth process) over at least a portion of the semiconductorsubstrate 104 and subsequently patterning the grown semiconductormaterial (e.g. using an etching process) to form the first protrusions110 extending from the first doped region 106. In some embodiments, thefirst epitaxial growth process may be molecular beam epitaxy (MBE),liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), selectiveepitaxial growth (SEG), or combinations thereof. Other epitaxial growthprocesses may also be possible. As described above, the source layers110 a may be formed by patterning a portion (e.g. an upper portion) ofthe first doped region 106. Consequently, the semiconductor material ofthe first doped region 106 and the source layers 110 a may be formedusing the same epitaxial growth process. Furthermore, in someembodiments, the semiconductor material of each of the source layers 110a, the channel layers 110 b, and the drain layers 110 c may be formedusing the same epitaxial growth process. However, in another embodiment,different epitaxial growth processes may be used to form thesemiconductor material of the source layers 110 a, the channel layers110 b, and the drain layers 110 c of the first protrusions 110.

As described above, the first doped region 106 and the first protrusions110 comprise doped semiconductor material. In an embodiment, dopants areintroduced into the semiconductor material of the first doped region106, the source layers 110 a, the channel layers 110 b, and the drainlayers 110 c as the semiconductor material of each of these features isgrown. As an example, during the epitaxial growth process of thesemiconductor material of the first doped region 106, precursors thatcomprise the desired dopants are placed in situ into the reaction vesselalong with the precursor reactants for the semiconductor material of thefirst doped region 106. As such, the dopants are introduced andincorporated into the semiconductor material of the first doped region106 to provide the first doped region 106 the desired conductivity anddopant concentration while the semiconductor material of the first dopedregion 106 is grown. Although the example presented above is directed tothe first doped region 106, a similar process may be used to introducedopants into the semiconductor material of the channel layers 110 b andthe drain layers 110 c as the semiconductor material of each of theselayers is grown.

Alternatively, in another embodiment, dopants may be introduced into thesemiconductor material of the first doped region 106, the source layers110 a, the channel layers 110 b, and the drain layers 110 c after thesemiconductor material of each layer is grown. As an example, thesemiconductor material of the first doped region 106 may be grownwithout the dopants, and an introduction process such as an implantationprocess or diffusion process is utilized to introduce the dopants intothe material of the first doped region 106 after this epitaxial growthprocess, but before growing the material of the channel layers 110 b.Once the dopants have been introduced into semiconductor material of thefirst doped region 106, an anneal process may be performed to activatethe dopants. Thereafter, the epitaxial growth of the semiconductormaterial of the channel layers 110 b may be commenced. Although theexample presented above is directed to the first doped region 106, asimilar process may be used to introduce dopants into the semiconductormaterial of the channel layers 110 b, and the drain layers 110 c afterthe semiconductor material of each of these layers is grown.

Referring to the second VGAA device 202, each of the second protrusions210 may be a multi-layer semiconductor substrate comprising a sourcelayer 210 a, a channel layer 210 b, and a drain layer 210 c. In aparticular embodiment, at least a portion of the source layers 210 a,the channel layers 210 b, and the drain layers 210 c of the secondprotrusions 210 form the source regions, channel regions, and drainregions of the second VGAA device 202, respectively.

The source layers 210 a, the channel layers 210 b, and the drain layers210 c may comprise any suitable semiconductor material, such as silicon,germanium, silicon germanium, combinations of these, or the like. Forexample, in an embodiment, each of the source layers 210 a, the channellayers 210 b, and the drain layers 210 c comprise doped silicon.However, in another embodiment, the channel layers 210 b may comprisedoped silicon, while the source layers 210 a and the drain layers 210 ccomprise doped silicon germanium. In some embodiments, the source layers210 a may be formed by patterning a portion (e.g. an upper portion) ofthe second doped region 206. Consequently, in such embodiments, thesource layers 210 a may comprise a similar semiconductor material as thesecond doped region 206.

The semiconductor material of each of the source layers 210 a, thechannel layers 210 b, and the drain layers 210 c also comprises dopantsthat cause the source layers 210 a, the channel layers 210 b, and thedrain layers 210 c to have the same conductivity as the second dopedregion 206 (e.g. the second conductivity), which is different from theconductivity of the first doped region 106. For example, the second VGAAdevice 202 may be a PMOS VGAA device and, consequently, the sourcelayers 210 a, the channel layers 210 b, and the drain layers 210 c ofthe second protrusions 210 may be doped with P-type dopants such asboron or gallium.

In an embodiment, the dopant concentration of the second doped region206, the source layers 210 a, and the drain layers 210 c may besubstantially equal to one another and may, at the same time, be greaterthan the dopant concentration of the channel layers 210 b. For example,the dopant concentration of the second doped region 206, the sourcelayers 210 a, and the drain layers 210 c may be in a range from about1×10¹⁹ cm ⁻³ to about 1×10²² cm⁻³ or even greater, while the dopantconcentration of the channel layers 210 b may be less than about 1×10¹⁸cm⁻³. In such an embodiment, the drain layers 210 c may be highly dopeddrain regions of the second VGAA device 202.

In another embodiment, the dopant concentration of the second dopedregion 206 and the source layers 210 a may be substantially equal toeach other and may, at the same time, be greater than the dopantconcentration of the channel layers 210 b and the drain layers 210 c.For example, the dopant concentration of the second doped region 206 andthe source layers 210 a may be in a range from about 1×10¹⁹ cm⁻³ toabout 1×10²² cm⁻³ or even greater, while the dopant concentration of thechannel layers 210 b and the drain layers 210 c may be less than about1×10¹⁸ cm⁻³. In such an embodiment, the drain layers 210 c may lowly ormoderately doped drain regions of the second VGAA device 202.

The second doped region 206 and the second protrusions 210 may be formedby epitaxially growing semiconductor material (e.g. using a secondepitaxial growth process) over at least a portion of the semiconductorsubstrate 104 and subsequently patterning the semiconductor material(e.g. using an etching process) to form the second protrusions 210extending from the second doped region 206. In some embodiments, thesecond epitaxial growth process may be molecular beam epitaxy (MBE),liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), selectiveepitaxial growth (SEG), or combinations thereof. Other epitaxial growthprocesses may also be possible. As described above, the source layers210 a may be formed by patterning a portion (e.g. an upper portion) ofthe second doped region 206. Consequently, the semiconductor material ofthe second doped region 206 and the source layers 210 a may be formedusing the same epitaxial growth process. Furthermore, in someembodiments, the material of each of the source layers 210 a, thechannel layers 210 b, and the drain layers 210 c may be formed using thesame epitaxial growth process. However, in another embodiment, differentepitaxial growth processes may be used to form the material of thesource layers 210 a, the channel layers 210 b, and the drain layers 210c of the second protrusions 210.

As described above, the second doped region 206 and the secondprotrusions 210 comprise doped semiconductor material. In an embodiment,dopants are introduced into the semiconductor material of the seconddoped region 206 and the second protrusions 210 as the semiconductormaterial of each of these features is grown. The description given abovein respect of introducing dopants into the semiconductor material of thefirst doped region 106, the source layers 110 a, the channel layers 110b, and the drain layers 110 c as the semiconductor material of each ofthese layers is grown may analogously apply to introducing dopants intothe semiconductor material of the second doped region 206, the sourcelayers 210 a, the channel layers 210 b, and the drain layers 210 c asthe semiconductor material of each of these layers is grown.

Alternatively, in another embodiment, dopants may be introduced into thesemiconductor material of the second doped region 206 and the secondprotrusions 210 after the semiconductor material of each layer is grown.The description given above in respect of introducing dopants into thesemiconductor material of the first doped region 106, the source layers110 a, the channel layers 110 b, and the drain layers 110 c after thesemiconductor material of each of these layers is grown may analogouslyapply to introducing dopants into the semiconductor material of thesecond doped region 206, the source layers 210 a, the channel layers 210b, and the drain layers 210 c after the semiconductor material of eachof these layers is grown.

As shown in FIG. 1A, the semiconductor device 100 may include firstsilicide regions 112 and second silicide regions 212. The first silicideregions 112 may be formed in portions of the first doped region 106proximal the source layers 110 a of the first protrusions 110 and may beused for integrated device contacts to the source layers 110 a of thefirst VGAA device 102. As an example, the first silicide regions 112 maybe disposed around the source layers 110 a of the first protrusions 110,e.g. when viewed in a top-down view. In like manner, the second silicideregions 212 may be formed in portions of the second doped region 206proximal the source layers 210 a of the second protrusions 210 and maybe used for integrated device contacts to the source layer 210 a of thesecond VGAA device 202. As an example, the second silicide regions 212may be disposed around the source layers 210 a of the second protrusions210, e.g. when viewed in a top-down view.

The first silicide regions 112 and the second silicide regions 212 maybe formed using a silicide process or other suitable methods, e.g. afterthe patterning process that forms the first protrusions 110 and thesecond protrusions 210. The first silicide regions 112 and the secondsilicide regions 212 may comprise one or more metal species that can beused to form silicide compounds of the first silicide regions 112 andthe second silicide regions 212. For example, the first silicide regions112 and the second silicide regions 212 can comprise silicide compoundsof titanium (e.g. TiSi₂), cobalt (e.g. CoSi₂), nickel (e.g. NiSi),combinations thereof, or the like.

As shown in FIG. 1A, the semiconductor device 100 may include first gatestacks 114 disposed adjacent to (e.g. surrounding) the channel layers110 b of the first protrusions 110, and second gate stacks 214 disposedadjacent to (e.g. surrounding) the channel layers 210 b of the secondprotrusions 210. For example, the first gate stacks 114 may encircle allsides of the channel layers 110 b of the first protrusions 110, whilethe second gate stacks 214 may encircle all sides of the channel layers210 b of the second protrusions 210, e.g. when viewed in a top-downview.

The first gate stacks 114 and the second gate stacks 214 may be disposedover a first spacer layer 116 formed over the first silicide regions 112and the second silicide regions 212 and around the source layers 110 aand 210 a of the first protrusions 110 and the second protrusions 210. Aportion of the first spacer layer 116 may also be disposed over theisolation feature 108, as shown in FIG. 1A. The first spacer layer 116may be used to provide an insulating layer that prevents the first gatestacks 114 from electrically contacting the underlying first dopedregion 106. The first spacer layer 116 also prevents the second gatestacks 214 from electrically contacting the underlying second dopedregion 206.

In some embodiments, the first spacer layer 116 may comprise adielectric material, such as silicon nitride, for example, formed usingany suitable process, such as, CVD, PVD, ALD, and the like. In someembodiments, the deposition of first spacer layer 116 may be a conformalprocess that is performed after the formation of the first silicideregions 112 and the second silicide regions 212. An etch back processmay be subsequently performed to remove excess portions of first spacerlayer 116 from the top surfaces of the first protrusions 110 and thesecond protrusions 210, from sidewalls of the drain layers 110 c and 210c, and from sidewalls of the channel layers 110 b and 210 b.

Each of the first gate stacks 114 may include a conformal first gatedielectric 114 a and a first gate electrode 114 b formed over first gatedielectric 114 a. In like manner, each of the second gate stack 214 mayinclude a conformal second gate dielectric 214 a and a second gateelectrode 214 b formed over second gate dielectric 214 a. The first gatedielectric 214 a and the second gate dielectric 214 a may includesilicon oxide, silicon nitride, or multilayers thereof. Additionally oralternatively, the first gate dielectric 114 a and the second gatedielectric 214 a may include a high-k dielectric material. In suchembodiments, first gate dielectric 114 a and the second gate dielectric214 a may include a metal oxide or a silicate of hafnium (Hf), aluminum(Al), zirconium (Zr), lanthanum (La), magnesium (Mg), barium (Ba),titanium (Ti), lead (Pb), combinations thereof, and the like. The firstgate dielectric 114 a and the second gate dielectric 214 a may be formedby molecular beam deposition (MBD), ALD, PECVD, and the like.

The first gate electrode 114 b and the second gate electrode 214 b mayinclude a metal-containing material such as titanium nitride (TiN),tantalum nitride (TaN), tantalum carbon (TaC), cobalt (Co), ruthenium(Ru), aluminum (Al), combinations thereof, multi-layers thereof, and thelike. In the example shown in FIG. 1A, the first gate electrode 114 bcomprises a multi-layer structure that is conformally formed over thefirst gate dielectric 114 a. However, in other embodiments, the firstgate electrode 114 b may comprise a single-layer structure. In theexample shown in FIG. 1A, the second gate electrode 214 b comprises asingle-layer structure that is conformally formed over the second gatedielectric 214 a. However, in other embodiments, the second gateelectrode 214 b may comprise a multi-layer structure.

The first gate electrode 114 b and second gate electrode 214 b in FIG.1A are conformally formed over the first gate dielectric 114 a and thesecond gate dielectric 214 a, respectively. However, in otherembodiments, the first gate electrode 114 b and the second gateelectrode 214 b may not be a conformal structure and, instead, may beformed using a suitable deposition process such as MBD, ALD, PECVD, andthe like. In such embodiments, an etch back process may be performed toremove excess portions of the first gate electrode 114 b from topsurfaces of the first protrusions 110 and from sidewalls of the drainlayers 110 c of the first protrusions 110. This etch back process mayalso remove excess portions of the second gate electrode 214 b from topsurfaces of the second protrusions 210 and from sidewalls of the drainlayers 210 c of the second protrusions 210.

The semiconductor device 100 may further include a second spacer layer118 a, 118 b disposed over the first gate stack 114 and the second gatestack 214. The second spacer layer 118 a, 118 b may comprise an oxidelayer 118 a (e.g. silicon oxide or silicon dioxide) and/or a nitridelayer 118 b (e.g. silicon nitride). The second spacer layer 118 a, 118 bmay be formed using any suitable process, such as, CVD, PVD, ALD, andthe like. An etch back process may be performed to remove excessportions of the second spacer layer 118 from the top surfaces of thefirst protrusions 110 and the second protrusions 210, and from at leasta portion of the sidewalls of the drain layers 110 c and 210 c of thefirst protrusions 110 and the second protrusions 210, as shown in FIG.1A. Accordingly, the top surfaces of the drain layers 110 c and 210 cand at least a portion of the sidewalls of the drain layers 110 c and210 c may be exposed and subjected to the process flow steps thatfollow.

In the process steps that follow, the drain layers 110 c of the firstprotrusions 110 and the drain layers 210 c of the second protrusions 210may be enlarged using, for example, an epitaxial growth process. Thedescription that follows shows an example of epitaxially growing thedrain layers 110 c of the first protrusions 110 prior to epitaxiallygrowing the drain layers 210 c of the second protrusions 210. However,in another embodiment, the drain layers 110 c of the first protrusions110 may be epitaxially grown after epitaxially growing the drain layers210 c of the second protrusions 210. In yet another embodiment, thedrain layers 110 c of the first protrusions 110 may be epitaxiallygrown, while the drain layers 210 c of the second protrusions 210 arekept without enlargement. In still another embodiment, the drain layers210 c of the second protrusions 210 may be epitaxially grown, while thedrain layers 110 c of the first protrusions 110 are kept withoutenlargement. The relevant process flow steps presented in thedescription that follows may be applied to these other embodiments.

As shown in FIG. 1B, a first hard mask 120 may be formed (e.g.conformally formed) over the second spacer layer 118, the firstprotrusions 110, and the second protrusions 210. The first hard mask 120may completely cover exposed surfaces of the second spacer layer 118 a,118 b, the first protrusions 110, and the second protrusions 210.Consequently, the first hard mask 120 may cover the exposed sidewalls ofthe drain layers 110 c of the first protrusions 110 and the exposedsidewalls of the drain layers 210 c of the second protrusions 210.

The first hard mask 120 may include an oxide layer 120 a (e.g.comprising silicon oxide or silicon dioxide) and a nitride layer 120 b(e.g. comprising silicon nitride) formed over the oxide layer 120 a. Theoxide layer 120 a and the nitride layer 120 b of the first hard mask 120may be formed using a suitable process such as chemical vapordeposition, plasma enhanced chemical vapor deposition, atomic layerdeposition, or the like. However, other suitable methods of forming theoxide layer 120 a and the nitride layer 120 b of the first hard mask 120may be utilized. The first hard mask 120 may be formed to a thickness ofbetween about 2 nm and about 60 nm, such as about 40 nm.

Once the first hard mask 120 has been formed, a portion of the firsthard mask 120 may be removed in order to expose the drain layers 110 cof the first protrusions 110, while keeping the drain layers 210 c ofthe second protrusions 210 covered. In other words, the first hard mask120 may be patterned to expose sidewalls of the drain layers 110 c ofthe first protrusions 110 and portions of the second spacer layer 118disposed over the first gate stacks 114, while a remaining portion ofthe first hard mask 120 continues to cover sidewalls of the drain layers210 c of the second protrusions 210 and portions of the second spacerlayer 118 disposed over the second gate stacks 214. This step isillustrated in FIG. 1C. In an embodiment, a masking and etching process(e.g. dry and/or wet etch process) may be used to expose sidewalls ofthe drain layers 110 c of the first protrusions 110 and portions of thesecond spacer layer 118 disposed over the first gate stacks 114.However, it should be understood that other suitable methods of removinga portion of the first hard mask 120 may be utilized in otherembodiments.

Referring to FIG. 1D, a third epitaxial growth process 122 may beperformed to enlarge the drain layers 110 c of the first protrusions110, thereby forming first enlarged drain regions 124 over exposedsurfaces of the drain layers 110 c of the first protrusions 110. Thethird epitaxial growth process 122 may be a low-temperature epitaxialgrowth process, e.g. performed at a temperature in a range from about400° C. to about 650° C., such as about 465° C. The third epitaxialgrowth process 122 may be molecular beam epitaxy (MBE), liquid phaseepitaxy (LPE), vapor phase epitaxy (VPE), selective epitaxial growth(SEG), or combinations thereof. In an embodiment, the third epitaxialgrowth process 122 may be performed for a time duration in a range fromabout 2 minutes to about 90 minutes (e.g. about 15 minutes). This mayresult in the first enlarged drain regions 124 having a thickness T1 ina range from about 1 nm to about 50 nm (e.g. about 10 nm), althoughother thicknesses and time durations may be possible. The thirdepitaxial growth process 122 may include the use of one or more processgases and one or more carrier gases. In an embodiment, the one or moreprocess gases may include silicon chloride hydride (SiCl₂H₂), silane(SiH₄), phosphine (PH₃), combinations thereof, or the like. The one ormore carrier gases may include nitrogen (N₂) and/or hydrogen (H₂). Underthe process conditions described above, the third epitaxial growthprocess 122 may have a growth rate in a range from about 0.5 nm perminute to about 3 nm per minute (e.g. about 1 nm per minute).

The first enlarged drain regions 124 may comprise doped semiconductormaterial having the same conductivity as the first doped region 106 andthe drain layers 110 c (e.g. the first conductivity). The dopantconcentration of the first enlarged drain regions 124 may besubstantially equal to the dopant concentration of the first dopedregion 106. In an embodiment, dopants are introduced into thesemiconductor material of the first enlarged drain regions 124 as thesemiconductor material of the first enlarged drain regions 124 is grown.The description given above in respect of introducing dopants into thesemiconductor material of the first doped region 106, the source layers110 a, the channel layers 110 b, and the drain layers 110 c as thesemiconductor material of each of these layers is grown may analogouslyapply to introducing dopants into the semiconductor material of thefirst enlarged drain regions 124 as the semiconductor material of thefirst enlarged drain regions 124 is grown.

Alternatively, in another embodiment, dopants may be introduced into thesemiconductor material of the first enlarged drain regions 124 after thesemiconductor material of the first enlarged drain regions 124 is grown.The description given above in respect of introducing dopants into thesemiconductor material of the first doped region 106, the source layers110 a, the channel layers 110 b, and the drain layers 110 c after thesemiconductor material of each of these layers is grown may analogouslyapply to introducing dopants into the semiconductor material of thefirst enlarged drain regions 124 after the semiconductor material of thefirst enlarged drain regions 124 is grown.

As described above, the third epitaxial growth process 122 may formsemiconductor material on exposed surfaces of the drain layers 110 c.These exposed surfaces of the drain layers 110 c include the exposedsidewalls and top surfaces of the drain layers 110 c. The growth of thesemiconductor material may proceed in a lateral direction (e.g.laterally away from the sidewalls of the drain layers 110 c), in avertical direction (e.g. in a direction away from the semiconductorsubstrate 104), or a combination thereof (e.g. in an oblique direction).

FIG. 2A shows a top-down view of the drain layers 110 c and the firstenlarged drain regions 124 in an embodiment where the first protrusions110 are shaped as nanowires. FIG. 2B shows the orientation of thelattice planes (expressed as Miller indices) for various surfaces of oneof the drain layers 110 c, when the drain layer 110 c is viewed in atop-down view.

The cross-sectional view of the first enlarged drain regions 124 and thedrain layers 110 c shown in FIG. 1D may be a taken along the line A-A′in FIG. 2A. A magnified cross-sectional view of the first enlarged drainregions 124 and the drain layers 110 c of the first protrusions 110taken along the line A-A′ in FIG. 2A is illustrated in FIG. 2C. Amagnified cross-sectional view of the first enlarged drain regions 124and the drain layers 110 c of the first protrusions 110 taken along theline B-B′ in FIG. 2A is illustrated in FIG. 2D.

As shown in FIGS. 2B, 2C, and 2D, various surfaces of the drain layers110 c may have different lattice plane orientations. The growth ofsemiconductor material on a surface of the drain layers 110 c may dependon the lattice plane orientation of the surface. For example, the growthrate of semiconductor material on a surface having a lattice planeorientation (100) may be greater than the growth rate of semiconductormaterial on a surface having a lattice plane orientation (110).Furthermore, the growth rate of semiconductor material on a surfacehaving a lattice plane orientation (110) may be greater than the growthrate of semiconductor material on a surface having a lattice planeorientation (111). For example, for the third epitaxial growth process122, the growth rate of semiconductor material on a surface having alattice plane orientation (110) may be in an upper range of theaforementioned range of about 0.5 nm per minute to about 3 nm per minute(e.g. about 1.5 nm per minute to about 3 nm per minute), while thegrowth rate of semiconductor material on a surface having a latticeplane orientation (111) may be in a lower range of the aforementionedrange of about 0.5 nm per minute to about 3 nm per minute (e.g. about0.5 nm per minute to about 1.5 nm per minute). Consequently, the thirdepitaxial growth process 122 may cause semiconductor material to grow onexposed surfaces of the drain layers 110 c such that the first enlargeddrain regions 124 comprise various facets (or faces) F1 to F6 (shown inFIG. 2D) having various orientations and subtending various angles withrespect to a reference line R (e.g. a horizontal reference line). As anexample, facets F4, F5, and F6 of the first enlarged drain regions 124proximal bottom regions 110 cb of the drain layers 110 c may extend adistance b from sidewalls of the drain layers 110 c. In someembodiments, the distance b may be in a range from about 0 nm to about50 nm, such as in a range from about 10 nm to about 40 nm, e.g. about 25nm. Furthermore, an angle c subtended between these facets F4, F5, andF6 of the first enlarged drain regions 124 and the reference line R(e.g. horizontal reference line) may be in a range from about 0 degreesto about 90 degrees, e.g. in a range from about 30 degrees to about 60degrees, e.g. in a range from about 35 degrees to about 55 degrees.

As described above, the third epitaxial growth process 122 may beperformed for a time duration in a range from about 10 minutes to about90 minutes (e.g. about 15 minutes). Depending on this time duration, thefirst enlarged drain region 124 formed over exposed surfaces of a firstdrain layer 110 c 1 may or may not physically contact the first enlargeddrain region 124 formed over exposed surfaces of a second drain layer110 c 2 laterally adjacent to the first drain layer 110 c 1. Forexample, if the third epitaxial growth process 122 is applied for alonger duration of time (e.g. greater than about 15 minutes), the firstenlarged drain region 124 formed over exposed surfaces of the firstdrain layer 110 c 1 may physically contact the first enlarged drainregion 124 formed over exposed surfaces of a second drain layer 110 c 2laterally adjacent to the first drain layer 110 c 1 (e.g. as shown inFIGS. 2C and 2D). However, in an embodiment where the third epitaxialgrowth process 122 is applied for a shorter duration of time (e.g. lessthan about 15 minutes), the first enlarged drain region 124 formed overexposed surfaces of the first drain layer 110 c 1 may not physicallycontact the first enlarged drain region 124 formed over exposed surfacesof a second drain layer 110 c 2 laterally adjacent to the first drainlayer 110 c 1. In the embodiment where the first enlarged drain regions124 of adjacent drain layers 110 c physically contact each other, athickness T2 (shown in FIG. 2D) of the region at which the firstenlarged drain regions 124 physically contact each other may be in arange from about 1 nm to about 50 nm, e.g. in a range from about 10 nmto about 40 nm, e.g. about 25 nm.

Referring to FIG. 1E, the process flow continues with masking the firstenlarged drain regions 124 (e.g. with a second hard mask 126) andremoving the portion of the first hard mask 120 disposed over the drainlayers 210 c of the second protrusions 210. This may be accomplished bydepositing (e.g. by spin-on coating, chemical vapor deposition, plasmaenhanced chemical vapor deposition) the second hard mask 126 over thefirst enlarged drain regions 124 and the portion of the first hard mask120 disposed over the drain layers 210 c of the second protrusions 210.The second hard mask 126 may comprise similar materials as the firsthard mask 120. Subsequently, a planarizing process (e.g. a chemicalmechanical polishing process) may be performed to planarize the secondhard mask 126 and expose the portion of the first hard mask 120 disposedover the drain layers 210 c of the second protrusions 210. Followingthis, an etching process (e.g. a wet and/or dry etch process) may beperformed to remove the portion of the first hard mask 120 disposed overthe drain layers 210 c of the second protrusions 210, thereby exposingthe drain layers 210 c of the second protrusions 210, as shown in FIG.1E. The planarizing process and the etching process performed on thefirst hard mask 120 are not shown in the process flow for the sake ofbrevity.

Referring to FIG. 1F, a fourth epitaxial growth process 222 may beperformed to enlarge the drain layers 210 c of the second protrusions210, thereby forming second enlarged drain regions 224 over exposedsurfaces of the drain layers 210 c. The fourth epitaxial growth process222 may be a low-temperature epitaxial growth process performed at atemperature in a range from about 400° C. to about 650° C., such asabout 465° C. The fourth epitaxial growth process 222 may be molecularbeam epitaxy (MBE), liquid phase epitaxy (LPE), vapor phase epitaxy(VPE), selective epitaxial growth (SEG), or combinations thereof. In anembodiment, the fourth epitaxial growth process 222 may be performed fora time duration in a range from about 10 minutes to about 90 minutes(e.g. about 15 minutes). This may result in the second enlarged drainregions 224 having a thickness T3 in a range from about 1 nm to about 50nm (e.g. about 10 nm), although other thicknesses and time durations maybe possible. The fourth epitaxial growth process 222 may include the useof one or more process gases and one or more carrier gases. In anembodiment, the one or more process gases of the fourth epitaxial growthprocess 222 may include silicon chloride hydride (SiCl₂H₂), silane(SiH₄), germane (GeH₄), diborane (B₂H₆), combinations thereof, or thelike. The one or more carrier gases may include nitrogen (N₂) and/orhydrogen (H₂). Under the process conditions described above, the fourthepitaxial growth process 222 may have a growth rate in a range fromabout 0.5 nm per minute to about 3 nm per minute (e.g. about 1 nm perminute).

The second enlarged drain regions 224 may comprise doped semiconductormaterial having the same conductivity as the second doped region 206(e.g. the second conductivity). The dopant concentration of the secondenlarged drain regions 224 may be substantially equal to the dopantconcentration of the second doped region 206. In an embodiment, dopantsare introduced into the semiconductor material of the second enlargeddrain regions 224 as the semiconductor material of the second enlargeddrain regions 224 is grown. The description given above in respect ofintroducing dopants into the semiconductor material of the first dopedregion 106, the source layers 110 a, the channel layers 110 b, and thedrain layers 110 c as the semiconductor material of each of these layersis grown may analogously apply to introducing dopants into thesemiconductor material of the second enlarged drain regions 224 as thesemiconductor material of the second enlarged drain regions 224 isgrown.

Alternatively, in another embodiment, dopants may be introduced into thesemiconductor material of the second enlarged drain regions 224 afterthe semiconductor material of the second enlarged drain regions 224 isgrown. The description given above in respect of introducing dopantsinto the semiconductor material of the first doped region 106, thesource layers 110 a, the channel layers 110 b, and the drain layers 110c after the semiconductor material of each of these layers is grown mayanalogously apply to introducing dopants into the semiconductor materialof the second enlarged drain regions 224 after the semiconductormaterial of the second enlarged drain regions 224 is grown.

As described above, the fourth epitaxial growth process 222 may formsemiconductor material on exposed surfaces of the drain layers 210 c.These exposed surfaces of the drain layers 210 c include the exposedsidewalls and top surfaces of the drain layers 210 c. The growth of thesemiconductor material may proceed in a lateral direction (e.g.laterally away from the sidewalls of the drain layers 210 c), in avertical direction (e.g. in a direction away from the semiconductorsubstrate 104), or a combination thereof (e.g. in an oblique direction).

As described above in respect of the drain layers 110 c of the firstprotrusions 110, various surfaces of the drain layers 110 c may havedifferent lattice plane orientations that can affect the growth ofsemiconductor material on these surfaces. In a similar manner, varioussurfaces of the drain layers 210 c of the second protrusions 210 mayhave different lattice plane orientations (similar to the orientationsshown in FIG. 2B). The growth of semiconductor material on a surface ofthe drain layers 210 c may depend on the lattice plane orientation ofthe surface. For example, the growth rate of semiconductor material on asurface having a lattice plane orientation (100) may be greater than thegrowth rate of semiconductor material on a surface having a latticeplane orientation (110). Furthermore, the growth rate of semiconductormaterial on a surface having a lattice plane orientation (110) may begreater than the growth rate of semiconductor material on a surfacehaving a lattice plane orientation (111). For example, for the fourthepitaxial growth process 222, the growth rate of semiconductor materialon a surface having a lattice plane orientation (110) may be in an upperrange of the aforementioned range of about 0.5 nm per minute to about 3nm per minute (e.g. about 1.5 nm per minute to about 3 nm per minute),while the growth rate of semiconductor material on a surface having alattice plane orientation (111) may be in a lower range of theaforementioned range of about 0.5 nm per minute to about 3 nm per minute(e.g. about 0.5 nm per minute to about 1.5 nm per minute). Consequently,the fourth epitaxial growth process 222 may cause semiconductor materialto grow on exposed surfaces of the drain layers 210 c such that thesecond enlarged drain regions 224 comprise various facets (or faces)having various orientations and subtending various angles with respectto a reference (much like the facets F1 to F6 of the first enlargeddrain regions 124, shown in FIG. 2D). Similarly, facets of the secondenlarged drain regions 224 proximal bottom regions of the drain layers210 c may extend by a distance from sidewalls of the drain layers 210 c.In some embodiments, this distance may be in a similar range as thedistance b described above in respect of the first enlarged drainregions 124. However, as described above, the second protrusions 210 maybe a part or portion of a PMOS VGAA device. In practice, P-typeepitaxial crystallization may be easier to perform that N-type epitaxialcrystallization. This can result in the distance between sidewalls ofthe drain layers 210 c and facets of the second enlarged drain regions224 proximal bottom regions of the drain layers 210 c being smaller thanthe above-described distance b between sidewalls of the drain layers 110c and facets of the first enlarged drain regions 124 proximal bottomregions of the drain layers 110 c. However, an angle subtended betweenthese facets of the second enlarged drain regions 224 and a referenceline R may be in a similar range as and may be substantially equal tothe angle c described above in relation to the first enlarged drainregions 124.

As described above, the fourth epitaxial growth process 222 may beperformed for a time duration in a range from about 10 minutes to about90 minutes (e.g. about 15 minutes). Depending on this time duration, thesecond enlarged drain region 224 formed over exposed surfaces of a firstdrain layer 210 c may or may not physically contact the second enlargeddrain region 224 formed over exposed surfaces of a second drain layer210 c laterally adjacent to the first drain layer 210 c. In anembodiment where physical contact is made between adjacent secondenlarged drain regions 224, a thickness of the region at which thesesecond enlarged drain regions 224 physically contact may besubstantially equal to the thickness T2 (shown in FIG. 2D) describedabove in respect of the first enlarged drain regions 124.

Referring to FIG. 1G, the second hard mask 126 disposed over the firstenlarged drain regions 124 may be removed (e.g. by an etching process)to expose the first enlarged drain regions 124 and the second enlargeddrain regions 224.

Referring to FIG. 1H, the process flow may be continued (e.g. inmultiple process flow steps) to form a first drain contact 128 over thefirst enlarged drain regions 124, and a second drain contact 228 overthe second enlarged drain regions 224. The first drain contact 128 mayinclude a first drain silicide 128 c disposed over the first enlargeddrain regions 124, and first conductive layers 128 b and 128 a disposedover the first drain silicide 128 c. The first drain silicide 128 c mayinclude similar materials as the first silicide regions 112. The firstconductive layers 128 b and 128 a may comprise a conductive materialsuch as copper, tungsten, or the like. The second drain contact 228 mayinclude a second drain silicide 228 c disposed over the second enlargeddrain regions 224, and second conductive layers 228 b and 228 a disposedover the second drain silicide 228 c. The second drain silicide 228 cmay include similar materials as the second silicide regions 212. Thesecond conductive layers 228 b and 228 a may comprise a conductivematerial such as copper, tungsten, or the like.

Following the manufacture of the structure shown in FIG. 1H, dielectricmaterial (e.g. comprising an oxide and/or a nitride) may be depositedover and may fully cover the first drain contact 128 and the seconddrain contact 228, e.g. on all sides of the first drain contact 128 andthe second drain contact 228. The dielectric material fully covering thefirst drain contact 128 and the second drain contact 228 may, as anexample, form an interlayer dielectric (ILD) layer of the semiconductordevice 100.

An effect provided by the process flow illustrated in FIGS. 1A and 1H isa larger contact area between the first drain contact 128 and the drainregions of the first VGAA device 102 compared to an NMOS VGAA devicewhere the first enlarged drain regions 124 are absent (hereinafterreferred to as a conventional NMOS VGAA device only for the sake ofbrevity and convenience). Similarly, the process flow illustrated inFIGS. 1A and 1H leads to a larger contact area between the second draincontact 228 and the drain regions of the second VGAA device 202 comparedto a PMOS VGAA device where the second enlarged drain regions 224 areabsent (hereinafter referred to as a conventional PMOS VGAA device onlyfor the sake of brevity and convenience). For example, in an embodimentwhere the first protrusions 110 and the second protrusions 210 arearranged as 2×3 matrices, a contact area between the first drain contact128 and the first enlarged drain regions 124 may be in a range fromabout 3000 nm² to about 4000 nm² (e.g. about 3500 nm²). A contact areabetween the second drain contact 228 and the second enlarged drainregions 224 may be in a similar range. In comparison, a contact areabetween the drain contact and drain regions of the conventional NMOSVGAA device and the conventional PMOS VGAA device may be in a range fromabout 1000 nm² to about 2000 nm² (e.g. about 1600 nm²). This increase incontact area between the drain contact and drain regions of the firstVGAA device 102 and the second VGAA device 202 in turn leads to lowercontact resistances in the first VGAA device 102 and the second VGAAdevice 202 as well as a larger drain pad landing for the first VGAAdevice 102 and the second VGAA device 202. The larger drain pad landingfor the first VGAA device 102 and the second VGAA device 202 leads tobetter control of drain pad enclosure windows for the first VGAA device102 and the second VGAA device 202. It is noted that the contactresistances in the first VGAA device 102 and the second VGAA device 202may be reduced further by judiciously selecting the semiconductormaterials of the first enlarged drain region 124 and the second enlargeddrain region 224. For example, in an embodiment where the semiconductormaterials of the first enlarged drain region 124 and the second enlargeddrain region 224 comprise both silicon and germanium, a higher germaniumconcentration relative to silicon can further reduce the contactresistances in the first VGAA device 102 and the second VGAA device 202.In another example, the semiconductor materials of the first enlargeddrain region 124 and the second enlarged drain region 224 may be devoidof silicon and this can also result in reduced contact resistances inthe first VGAA device 102 and the second VGAA device 202. As anillustration, the first enlarged drain region 124 and the secondenlarged drain region 224 may comprise pure germanium, a group III-Vsemiconductor material, or a combination thereof (e.g. a multilayerstructure comprising a layer of pure germanium and another layer of agroup III-V semiconductor material). In this example, the contactresistances in the first VGAA device 102 and the second VGAA device 202is also reduced.

FIGS. 3A and 3B show plan views (e.g. top-down views) of the firstprotrusions 110 or the second protrusions 210. Also shown in FIGS. 3Aand 3B are the first enlarged drain regions 124 or the second enlargeddrain regions 224 formed over exposed sidewalls of the drain layers 110c or 210 c, respectively. As shown in FIG. 3A, the first protrusions 110or the second protrusions 210 may be shaped as nanowires (e.g. having asubstantially circular shape) having a diameter D in a range from about5 nm to about 20 nm, e.g. about 10 nm. In the embodiment of FIG. 3B,however, the first protrusions 110 or the second protrusions 210 may beshaped as bars or fins that have a first lateral extent L1 in a firstdirection and a second lateral extent L2 in a second directionsubstantially perpendicular to the first direction. As shown in FIG. 3B,the first lateral extent L1 is different from (e.g. smaller than) thesecond lateral extent L2. In an embodiment the first lateral extent L1may be in a range from about 5 nm to about 20 nm (e.g. about 10 nm),while the second lateral extent L2 may be in a range from about 5 nm toabout 2000 nm (e.g. about 60 nm). In some embodiments, the secondlateral extent L2 may be larger than about 2000 nm.

According to an embodiment presented herein, a method of manufacturing avertical gate all around device comprises: exposing a top surface andsidewalls of a first portion of a protrusion extending from a dopedregion, wherein a second portion of the protrusion is surrounded by agate stack; and enlarging the first portion of the protrusion using anepitaxial growth process.

According to an embodiment presented herein, a method of manufacturing avertical gate all around device comprises: forming a first doped regionover a substrate, the first doped region having a first conductivity anda first protrusion extending away from the substrate; forming a seconddoped region laterally adjacent to the first doped region, the seconddoped region having a second conductivity different from the firstconductivity and a second protrusion extending away from the substrate;exposing surfaces of a drain layer of the first protrusion, wherein achannel layer of the first protrusion is surrounded by a first gatestack; exposing surfaces of a drain layer of the second protrusion,wherein a channel layer of the second protrusion is surrounded by asecond gate stack; and epitaxially growing semiconductor material overthe exposed surfaces of the drain layers of the first protrusion and thesecond protrusion.

According to an embodiment presented herein, a vertical gate all arounddevice comprises: a semiconductor substrate; a doped region over thesemiconductor substrate; a protrusion extending from the doped regionaway from the semiconductor substrate, the protrusion comprising asource layer proximal the doped region, a channel layer disposed overthe source layer, and a drain layer disposed over the channel layer; agate stack encircling the channel layer of the protrusion; and anenlarged drain region disposed over a top surface and extending fromsidewalls of the drain layer of the protrusion.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: forming a doped region in asemiconductor substrate; forming a protrusion extending from the dopedregion; depositing a first spacer layer over the doped region, the firstspacer layer surrounding a first portion of the protrusion; forming agate stack over the first spacer layer, the gate stack surrounding asecond portion of the protrusion; and epitaxially growing an epitaxialregion over a third portion of the protrusion, the epitaxial regioncontacting a top surface and side surfaces of the protrusion, theepitaxial region having an octagonal shape in a first cross-sectionalview.
 2. The method of claim 1, wherein the epitaxial region isepitaxially grown surrounding a first source/drain region of theprotrusion, wherein the first source/drain region comprises the thirdportion of the protrusion.
 3. The method of claim 2, further comprisingdoping the doped region, the first source/drain region, and a secondsource/drain region of the protrusion to a dopant concentration from1×10¹⁹ cm⁻³ to 1×10²² cm⁻³ and doping a channel region of the protrusionto a dopant concentration less than 1×10¹⁸ cm⁻³.
 4. The method of claim2, further comprising doping the doped region and a second source/drainregion of the protrusion to a dopant concentration from 1×10¹⁹ cm ⁻³ to1×10²² cm ⁻³ and doping a channel region of the protrusion and the firstsource/drain region to a dopant concentration less than 1×10¹⁸ cm⁻³. 5.The method of claim 1, wherein forming the gate stack comprises:depositing a gate dielectric layer over the first spacer layer and theprotrusion; depositing a gate electrode over the gate dielectric layer;and etching back the gate electrode and the gate dielectric layer toexpose the top surface and the side surfaces of the protrusion.
 6. Themethod of claim 5, further comprising: depositing a second spacer layerover the gate stack; and etching back the second spacer layer to exposethe third portion of the protrusion.
 7. The method of claim 1, whereinthe epitaxial region has a rectangular shape in a second cross-sectionalview orthogonal to the first cross-sectional view.
 8. A methodcomprising: forming a first doped region over a semiconductor substrate;forming a first protrusion extending from the first doped region;forming a first gate stack surrounding the first protrusion; etching thefirst gate stack to expose a first portion of the first protrusion;depositing a first spacer surrounding the first portion of the firstprotrusion; etching the first spacer to expose a second portion of thefirst protrusion; and epitaxially growing a first semiconductor materialsurrounding the second portion of the first protrusion, the firstsemiconductor material having a hexagonal shape in a top-down view. 9.The method of claim 8, wherein forming the first doped region andforming the first protrusion comprises epitaxially growing asemiconductor material over the semiconductor substrate and patterningthe semiconductor material.
 10. The method of claim 9, wherein dopantsare introduced into the semiconductor material as the semiconductormaterial is epitaxially grown.
 11. The method of claim 9, whereindopants are implanted into the semiconductor material after thesemiconductor material is epitaxially grown.
 12. The method of claim 8,wherein the first protrusion comprises a first source region, a firstchannel region, and a first drain region, wherein forming the firstprotrusion comprises using different epitaxial growth processes to formsemiconductor materials in each of the first source region, the firstchannel region, and the first drain region.
 13. The method of claim 8,further comprising after forming the first protrusion, using a silicideprocess to form a first silicide region in the first doped regionadjacent the first protrusion.
 14. The method of claim 8, furthercomprising, prior to forming the first gate stack: depositing a secondspacer over the first protrusion and the first doped region; and etchingback the second spacer to expose a third portion of the firstprotrusion, wherein the first gate stack is formed surrounding the thirdportion of the first protrusion.
 15. A method comprising: forming afirst doped region over a semiconductor substrate; forming a seconddoped region over the semiconductor substrate, the second doped regionbeing laterally adjacent the first doped region; forming a firstprotrusion extending from the first doped region; forming a secondprotrusion extending from the second doped region; depositing a firstgate stack over the first protrusion; etching back the first gate stackto expose a first portion of the first protrusion; epitaxially growing afirst epitaxial semiconductor material from the first portion of thefirst protrusion, the first epitaxial semiconductor material having anoctagonal shape in a first cross-sectional plane; depositing a secondgate stack over the second protrusion; etching back the second gatestack to expose a second portion of the second protrusion; andepitaxially growing a second epitaxial semiconductor material from thesecond portion of the second protrusion, the second epitaxialsemiconductor material having an octagonal shape in the firstcross-sectional plane.
 16. The method of claim 15, further comprising:etching a recess between the first doped region and the second dopedregion; and depositing an insulating material in the recess to form anisolation feature.
 17. The method of claim 16, further comprisingforming a first spacer layer over the semiconductor substrate, the firstspacer layer extending from the first protrusion, over the isolationfeature, to the second protrusion, wherein the first gate stack and thesecond gate stack are deposited over the first spacer layer.
 18. Themethod of claim 17, further comprising forming a second spacer layerover the first gate stack and the second gate stack, the second spacerlayer physically contacting the first spacer layer, the second spacerlayer extending from a sidewall of the first gate stack to a sidewall ofthe second gate stack.
 19. The method of claim 18, wherein forming thesecond spacer layer comprises: depositing a nitride layer over the firstgate stack, the second gate stack, the first spacer layer, the firstprotrusion, and the second protrusion; depositing an oxide layer overthe nitride layer; and etching the oxide layer and the nitride layerback to expose the first protrusion and the second protrusion beforeepitaxially growing the first epitaxial semiconductor material and thesecond epitaxial semiconductor material.
 20. The method of claim 16,further comprising siliciding portions of the first doped region and thesecond doped region between the first protrusion and the secondprotrusion to form a silicide region, wherein the isolation featureextends through the silicide region.